[PATCH] D37406: [TailCall] Allow llvm.memcpy/memset/memmove to be tail calls when parent function return the intrinsics's first argument

[Wei Mi via llvm-commits]

On Thu, Sep 7, 2017 at 12:34 PM, Eli Friedman via Phabricator
<reviews at reviews.llvm.org> wrote:
> efriedma added inline comments.
>
>
> ================
> Comment at: llvm/trunk/lib/CodeGen/Analysis.cpp:569
> +  // Intrinsic like llvm.memcpy has no return value, but will return the
> +  // first argument if it is expanded as libcall.
> +  const CallInst *Call = cast<CallInst>(I);
> ----------------
> This is only true if the argument is specifically expanded to a libcall to the C library function "memcpy".  If the target expands it to some other library call (e.g., __aeabi_memcpy, like we do on Android), it isn't a tail call, and we miscompile.

Sorry about it. Plan to fix it using TLI.getLibcallName(RTLIB::MEMCPY)
like below. Does it look ok?

--- lib/CodeGen/Analysis.cpp (revision 309240)
+++ lib/CodeGen/Analysis.cpp (working copy)
@@ -565,6 +565,19 @@ bool llvm::returnTypeIsEligibleForTailCa
     return false;

   const Value *RetVal = Ret->getOperand(0), *CallVal = I;
+  // Intrinsic like llvm.memcpy has no return value, but will return the
+  // first argument if it is expanded as libcall.
+  const CallInst *Call = cast<CallInst>(I);
+  if (Intrinsic::ID IID = Call->getCalledFunction()->getIntrinsicID())
+    if (((IID == Intrinsic::memcpy &&
+          TLI.getLibcallName(RTLIB::MEMCPY) == StringRef("memcpy")) ||
+         (IID == Intrinsic::memmove &&
+          TLI.getLibcallName(RTLIB::MEMMOVE) == StringRef("memmove")) ||
+         (IID == Intrinsic::memset &&
+          TLI.getLibcallName(RTLIB::MEMSET) == StringRef("memset"))) &&
+        RetVal == Call->getArgOperand(0))
+      return true;
+
   SmallVector<unsigned, 4> RetPath, CallPath;
   SmallVector<CompositeType *, 4> RetSubTypes, CallSubTypes;

>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D37406
>
>
>